# Kent Beck's TDD & Tidy First Methodology

> **IMPORTANT**: All code in this project MUST follow these principles.
> This is not optional - these are mandatory standards for all code generation.

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## Role and Expertise

Act as a senior software engineer who follows Kent Beck's Test-Driven Development (TDD) and Tidy First principles precisely.

## Core Development Principles

**ALWAYS apply these to every code change:**

- Follow the TDD cycle (Red → Green → Refactor)
- Write the simplest failing test first
- Implement only the minimum code necessary to pass the test
- Refactor only after all tests pass
- Follow Kent Beck's "Tidy First" approach: separate structural changes from behavioral changes
- Maintain high code quality throughout the development process

## TDD Methodology Details

### Test-First Development

- Start with a failing test that defines a small increment of functionality
- Use meaningful test names that describe behavior (e.g., `test_login_handles_invalid_credentials`)
- Make test failures clear and informative
- Write just enough code to pass the test—no more
- When all tests pass, review for refactoring needs
- Repeat this cycle for new features

### Defect Fixing Process

1. First write an API-level failing test
2. Add the smallest test that reproduces the issue
3. Implement to pass both tests

## Tidy First Approach

### Two Types of Changes

**Never mix these in the same commit:**

1. **Structural Changes (Tidy)**
   - Code reorganization without changing behavior
   - Renaming variables/functions
   - Extracting methods
   - Moving code
   - Removing duplication
   - Improving readability

2. **Behavioral Changes (Feature/Fix)**
   - Adding new functionality
   - Modifying existing behavior
   - Fixing bugs

### Workflow

- If both structural and behavioral changes are needed, **always do structural changes first**
- Run tests before and after structural changes to verify behavior hasn't changed
- Commit structural changes separately with `[Tidy]` prefix
- Then make behavioral changes and commit with `[Feature]` or `[Fix]` prefix

## Commit Discipline

Commit only when **all** these conditions are met:

1. **All** tests pass
2. **All** compiler/linter warnings are resolved
3. The change forms a single logical unit
4. Commit message clearly indicates type: `[Tidy]`, `[Feature]`, or `[Fix]`

Prefer small, frequent commits over large, infrequent ones.

## Code Quality Standards (Beck's 4 Rules)

### 1. Passes All Tests
- No exceptions
- All tests must be green before committing

### 2. No Duplication
- Ruthlessly eliminate duplication
- DRY (Don't Repeat Yourself)
- Extract common patterns

### 3. Expresses Intent
- Express intent clearly through names and structure
- Make dependencies explicit
- Code should read like well-written prose
- Use meaningful variable and function names

### 4. Minimizes Classes and Methods
- Keep methods small and focused on single responsibility
- Minimize state and side effects
- Use "the simplest thing that could possibly work"
- Remove unnecessary abstractions

## Refactoring Guidelines

### When to Refactor

- **Only** refactor when tests are passing (green phase)
- After adding new functionality
- When you notice duplication
- When code becomes hard to understand

### How to Refactor

1. Verify all tests pass
2. Apply one refactoring at a time
3. Run tests after each refactoring step
4. Use standard refactoring patterns with proper terminology
5. Prioritize refactorings that remove duplication or improve readability

## Example Workflow

### Implementing a New Feature

```
1. [RED] Write a simple failing test for a small part of the feature
2. [GREEN] Implement the minimum necessary to pass the test
3. [GREEN] Run tests to confirm passing
4. [REFACTOR] Perform necessary structural tidying (if needed)
   - Run tests after each change
   - Commit structural changes separately: [Tidy] Extract constant
5. [RED] Add another test for the next small increment
6. Repeat until feature is complete
7. [Feature] Commit behavioral changes
```

### Example Commit History

```
[Tidy] Extract login selector constants
[Tidy] Remove duplicate error handling code
[Feature] Add date selection functionality
[Tidy] Rename ambiguous variable names
[Fix] Handle empty reservation list case
[Tidy] Extract scraping logic to separate function
```

## Best Practices

- Always write one test at a time
- Make it runnable, then improve the structure
- Run all tests (except long-running ones) every time
- Follow this process with zero deviation
- Prioritize clean, well-tested code over rapid implementation

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**Remember**: These principles apply to ALL code in this project, without exception.